The Edwards
aquifer of South Texas has a complex and highly heterogeneous flow
system. Integration of multiple data sets has the best chance of
providing an adequate glimpse of the nature of the heterogeneities
and their impact on aquifer performance. Karst has developed in
this carbonate aquifer in response to the interaction of structure
and gradient. Karst capture, favored by fractures of the Balcones
Fault Zone, has diverted surface-water flow from toward the Gulf
of Mexico into the subsurface and caused it to flow eastward and
discharge at Comal and San Marcos Springs. We mapped large troughs
in the potentiometric surface by grouping the large volume of historic-water-level
data according to aquifer stage. Cave orientations confirm a history
of karst capture at a smaller scale.

We are examining
the implications of these karst trends for interpreting natural
chemistry and introduced-contaminant distribution, as well as high-frequency
water-level records.